In general, the air pressure regulator is so constructed that a cylindrical support is secured to one outer surface of a body with interposition of a diaphragm, a retaining member being slidable within the cylindrical support is threaded on an adjustment screw rotatably mounted in said cylindrical support, there is provided between said retaining member and said diaphragm an adjustment spring, a resilient force of said adjustment spring is balanced with a pressure prevailing within a pressure chamber communicating with a secondary chamber and thereby an opening degree of a valve port defined between a primary chamber and said secondary chamber is varied to maintain a secondary pressure substantially at a constant level, and an adjustment knob connected to the adjustment screw for rotation integrally therewith is rotated to adjust a resilient force of the adjustment spring and thereby to adjust a set value of the secondary pressure.
Conventionally, the adjustment knob for such air pressure regulator of prior art has been adapted to be secured by means of set screws or the like to the adjustment screw and has made installation or dismounting for cleaning an inconveniently time-consuming task. To overcome such inconvenience, an improved arrangement has been proposed such that the adjustment knob is constructed in the form of a cylindrical component adapted to be rotated by means of a hexagonal coupling or the like integrally with the adjustment screw, said adjustment knob is provided with elastic lock claws depending from its upper wall substantially in parallel with its inner peripheral surface, on one hand, the cylindrical support is provided in its outer peripheral surface with a circumferential groove, on the other hand, so that said elastic lock claws are engaged into said circumferential groove by depressing the adjustment knob onto the cylindrical support and thereby said adjustment knob is rotatably mounted on said cylindrical support, and said adjustment knob is dismounted from said cylindrical support as said elastic lock claws are disengaged from said circumferential groove by pulling said adjustment knob. This improved construction is certainly advantageous in that the adjustment knob can be easily mounted on the cylindrical support merely depressing said adjustment knob onto said cylindrical support. However, when it is desired to dismount the adjustment knob from the cylindrical support, a relatively large force would be required to release the elastic lock claws from the circumferential groove and the operation of dismounting would be correspondingly troublesome. If an extent by which the elastic lock claws are engaged into the circumferential groove is adjusted to be relatively shallow in order to facilitate the operation of dismounting, there would occur an inconvenience such that the adjustment knob might be readily detached from the cylindrical support during rotation of said adjustment knob in its use.